LOUD AND CLEAR: If Giants fans want to be able to cheer Eli Manning and his teammates after a big victory Sunday, they way they did after last year’s playoff win over the Falcons (above), Steve Serby says the crowd at MetLife Stadium must be Superdome loud when Drew Brees and the Saints have the ball. Photo: Getty Images

LOUD AND CLEAR: If Giants fans want to be able to cheer Eli Manning and his teammates after a big victory Sunday, they way they did after last year’s playoff win over the Falcons (above), Steve Serby says the crowd at MetLife Stadium must be Superdome loud when Drew Brees and the Saints have the ball. (Getty Images)

When the Giants talk about All In, they mean a stadium shaking with a howling blue army — their 12th Man, its deafening roar thundering Sunday through a place that will unmistakably become Giants Stadium, no matter what they call it now, when the Saints come marching in.

The Giants won’t soon forget how the Superdome crowd has punctured their eardrums over the years, and now they are asking their fans to be anything but Saints, to help fan the flames of another Super Bowl run in their most desperate hour.

So when The Post asked Eli Manning what his message would be for Giants fans Sunday, he said:

“Be loud.

“When the Saints have the ball, that’s the time to start yelling at our defense and help them out.”

I asked defensive coordinator Perry Fewell if he has noticed how his pass rushers can feed off the crowd.

“They want to feed off the crowd, the crowd gets them rolling, and really, that’s what you call home-field advantage, right?” Fewell said. “And so sometimes we need them to inspire us.”

Sometimes, of course, the fans need the Giants to inspire them, the way they did against the Packers.

“We played with a lot of energy, and our crowd was fired up because we were playing well.” Chris Snee said.

It won’t be particularly cold. But it can be particularly hostile. It can’t be the Superdome. But maybe, as the champs dig deep to defend their championship, it can be the Superhome.

The message for Giants fans from Victor Cruz: “Make believe that we’re playing in the Dome, and make believe that that sound is gonna echo off the walls, so … just be as loud as you can, and make it as difficult as they can for their quarterback.”

The Giants would embrace a crowd as loud as the one that showed up for last season’s playoff victory over the Falcons.

“Everybody talks about New York fans being on your side one time, and then the next time they’re giving you crap,” Baas said. “But you know what? Sometimes, it’s deserved. But I feel like they always have our backs and they’re very loyal.”

Baas’ message for Giants fans: “It’s a home game, it’s our house. We need everybody on our side. We need them to be as raucous as they can, and be as loud as they can. Like any offense, if you can get ’em flustered and you’re not communicating well, it creates good opportunities for our defense, and you can see what our defense has done when those arise. [The fans are] very helpful to our success, so they need to be on their ‘A’ game. And so do we.”

Baas has witnessed how Jason Pierre-Paul and Company feed off the a veritable Monster of the Meadowlands.

“I mean, who wouldn’t feed off of a JPP chant, you know?” Baas said. “That’s football, that’s the excitement of it. … You get chills when you’re out there. … That’s just that energy. Like you said, they feed off of it.”

The Giants were run out of the Superdome in 2009 and again last season.

“It can be challenging trying to change protections, or change plays [when the crowd is loud],” Manning said. “So I think those type of things make it difficult. If you don’t have to do that a whole lot, it might not affect it as much.”

Can MetLife Stadium have that effect on opposing quarterbacks?

“Yeah, I think so,” Manning said. “When it gets fired up, and big plays and big circumstances, you definitely make it difficult to communicate.”

Cruz won’t miss the Mardi Gras atmosphere inside the Dome.

“It makes it pretty difficult when you try to make different checks at the line and you want everybody to hear you, and for you to potentially not be able to hear it at times or for you having to yell through the crowd, it gets difficult,” Cruz said.

Payback, from Giants fans.

“For the first time in a while, we’re playing that team here instead of in New Orleans,” David Diehl said. “That’s a huge thing for them, they got a high-pace offense that can score a lot of points and get up fast, and to have that Dome noise and that crowd into the games like they are, and to have to do it on a silent count with the different blitzes and stunts, and whether it was Gregg Williams and now Coach [Steve] Spagnuolo doing it, it puts a huge advantage for them. … So to be able to play them at home is something that we need to use to our advantage. We need to play fast, we need to play physical, and we need to get our fans into the game just like they do theirs.”

Spencer Paysinger’s message for Giants fans: “Bring your ‘A’ game and just be as loud as possible.”